The present invention relates to a plasma processing apparatus and a plasma processing method that utilize plasma.
Generally, in applying a patterning process with a depth on the order of several hundreds nanometers to several hundreds micrometers to a to-be-processed object as typified by a substrate including a thin film formed on its surface, a resist process is utilized. FIG. 16A to FIG. 16D illustrate an example thereof. Referring to FIG. 16A to FIG. 16D, a photosensitive resist 30 is applied to the surface of a to-be-processed object 29 (FIG. 16A). By applying light exposure thereto with an exposure apparatus and then performing development, the resist 30 can be patterned into a desired shape (FIG. 16B). Then, the to-be-processed object 29 is placed within a vacuum chamber and plasma is generated within the vacuum chamber. Then, an etching process is applied to the to-be-processed object 29 by using the resist 30 as a mask to pattern the surface of the to-be-processed object 29 into a desired shape (FIG. 16C). Finally, the resist 30 is removed using oxygen plasma or an organic agent to complete the process (FIG. 16D)
Resist processes as described above have played important roles in fabricating electronic devices such as semiconductor devices, since the resist processes are suitable for forming fine patterns with high accuracy. However, such resist processes have the drawback of complicacy of processes.
Therefore, there have been conducted studies for new processing methods without usage of resist processes. As an example, FIGS. 17 to 21 illustrate the structure of a plasma processing apparatus incorporating a micro-plasma source. FIG. 17 illustrates an exploded view of the micro-plasma source. The micro-plasma source is constituted by a ceramic outer plate 31, inner plates 31 and 33, an outer plate 34 and a plate-shaped electrode 35, all of which have a thickness of 1 mm. Further, the outer plates 31 and 34 are provided with an outer gas flow channel 36 and an outer gas ejecting port 37 while the inner plates 32 and 33 are provided with an inner gas flow channel 38 and an inner gas ejecting port 39. A material gas to be ejected from the inner gas ejecting port 39 is supplied from an inner gas supplying port 40 provided through the outer plate 31 to the inner gas flow channel 38 via through holes 41 provided through the inner plate 32 and the plate-shaped electrode 35.
Further, a material gas to be ejected from the outer gas ejecting port 37 is supplied from an outer gas supplying port 42 provided through the outer plate 31 to the outer gas flow channel 36 via through holes 43 provided through the inner plate 32, the inner plate 33, and the plate-shaped electrode 35. Further, the plate-shaped electrode 35 to be subjected to a high-frequency power supply thereto is inserted between the inner plates 32 and 33 and is wired to a power supply portion through a drawing portion 44.
FIG. 18 illustrates a plan view of the micro-plasma source, viewed from the side of the gas ejecting ports. There are provided the outer plate 31, the inner plates 32 and 33, the outer plate 34, and the plate-shaped electrode 35, wherein the outer gas ejecting ports 37 are provided between the outer plate 31 and the inner plate 32 and between the inner plate 33 and the outer plate 34 and the inner gas ejecting ports 39 are provided between the inner plate 32 and the plate-shaped electrode 35 and between the inner plate 33 and the plate-shaped electrode 35. The length e of the inner gas ejecting ports 39 in the line direction is 30 mm, and the length f of the outer gas ejecting ports 37 in the line direction is 36 mm, which is greater than the length e of the inner gas ejecting ports 39 in the line direction. The length g of the plate-shaped electrode 35 in the line direction is 30 mm.
FIG. 19 illustrates a cross-sectional view of a to-be-processed object 15 and the micro-plasma source, taken along a surface perpendicular to the to-be-processed object 15. The micro-plasma source is constituted by the ceramic outer plate 31, the inner plates 32 and 33, the outer plate 34, and the plate-shaped electrode 35, wherein the outer plates 31 and 34 are provided with the outer gas ejecting ports 37 while the inner plates 32 and 33 are provided with the inner gas ejecting ports 39. The plate-shaped electrode 35 is maintained at a ground electric potential while a counter electrode 46 to be fed with a high-frequency electric power is placed at a position opposing to the micro-plasma source. The inner gas ejecting ports 39 between the inner plate 32 and the plate-shaped electrode 35 and between the inner plate 33 and the plate-shaped electrode 35, which are opening portions of the micro-plasma source, have a fine line width of 0.05 mm.
In a plasma processing apparatus incorporating the micro-plasma source having the aforementioned structure, helium (He) is supplied from the inner gas ejecting ports and sulfur hexafluoride (SF6) is supplied from the outer gas ejecting ports while a high-frequency electric power is applied to the counter electrode 46, thus applying an etching process to a fine line-shaped portion of the to-be-processed object 15. This is because micro-plasma can be generated only near the inner gas ejecting ports 39 where helium is concentrated, by utilizing the difference of the tendency to cause electric discharge under pressures near the atmospheric pressure between helium and sulfur hexafluoride (helium tends to cause electric discharge more significantly than sulfur hexafluoride).
Japanese Unexamined Patent Publication No. 2004-111949 describes, in detail, the application of a line-shaped process to Si employed as a to-be-processed object, by utilizing a plate-shaped electrode having sharp-angular portions in a plasma processing apparatus incorporating a micro-plasma source having the aforementioned structure. Japanese Examined Patent Publication No. 3014111 describes characteristics of atmospheric-pressure glow plasma, particularly, etching.
By using the aforementioned plasma processing apparatus, it is possible to perform etching on Si used as a to-be-processed object 15 for about 120 seconds, for example, under a condition where as gas, He gas and SF6 gas are supplied to the gas flow channels 7 at 1000 sccm and 400 sccm, respectively, and a high-frequency electric power of 100 W is supplied thereto.
However, the plasma processing apparatus and method described as a conventional example have two issues. The first issue is as follows. That is, when a groove is formed in a to-be-processed portion of a to-be-processed object 15 through etching, the shape of the resultant groove does not have excellent verticality. The second issue is as follows. When the etching depth of the to-be-processed portion in the to-be-processed object 15 reaches a certain value, the etching is interrupted halfway therethrough. FIG. 20 illustrates one example of an etching shape resulted from processing for 120 seconds under the aforementioned plasma condition.
FIG. 20 is a cross-sectional view of the etching shape of a groove portion, wherein various parameters for evaluation of the etching shape are defined as follows. In assuming that the distance between the deepest portion of the groove portion and the surface W of the to-be-processed object is the etching depth Y, the position shallower than the pattern bottom by Y×0.8 is β1, the line width at the depth is defined as the line width X1 of the upper end portion of the groove portion, the position shallower than the pattern bottom by Y×0.2 is β2, and the line width at the depth is defined as the line width X2 of the bottom portion of the etched portion. Further, an angle α indicating the verticality is defined as the angle between the straight line β between β1 and β2 to each other and the surface W of the to-be-processed object.
Referring to FIG. 20, in performing a fine process with a depth on the order of several hundreds micrometers, the etching depth Y is 124 μm, the line width X1 of the upper end portion of the groove portion is 542 μm, and the line width X2 of the bottom portion of the groove portion is 214 μm. Accordingly, the angle α indicating the verticality of the shape of the groove portion is 24.3° (note that the transversal axis and the vertical axis in the figure have different orders). The equation for calculating the angle α is as follows.α=Arctan(2·(0.8Y−0.2Y)/(X1−X2))
FIG. 21 illustrates the dependence of the etching depth on the etching time. As can be seen from the figure, the etching was interrupted at an etching depth of about 280 μm in the depthwise direction.
In view of the aforementioned issues in the conventional art, it is an object of the present invention to provide plasma processing apparatus and method which are capable of applying plasma processes to desired to-be-finely-processed portions (to-be-processed portions) with depths on the order of several hundreds nanometers to several hundreds micrometers to provide etching shapes with excellent verticality without causing interruption of etching in the depthwise direction.